Dear Science: Why do we love our pets?

“It really is an amazing question,” said Clive Wynne, director of the Canine Science Collaboratory at Arizona State University.

Wynne has devoted his career to studying animal behavior and the evolutionary relationship between animals and people. He said it's easy to see why our pets would love us: “The success of dogs [and other domesticated creatures] on the surface of the Earth is entirely due to the fact that we take some level of care of them.”

In fact, some scientists have suggested that pets exhibit a form of parasitism — taking food and shelter from humans without offering much in return. “They argue that we love our pets because they have hoodwinked us into it,” Wynne said.

He doesn't buy that argument. (Then again, he is a dog owner — he's under the spell!) But he acknowledged there's no satisfying evolutionary explanation for that warm, gooey feeling we get when we look at our dogs and cats.

This love story started with dogs, our most ancient animal companions. Analysis of dog and wolf genomes, along with numerous discoveries of ancient bone, suggests that humans domesticated our canine friends somewhere between 13,000 and 30,000 years ago. Wynne thinks it's likely that the animals started out as wolves that scavenged from human garbage pits; those willing to get closer to people got more food, and they evolved to become tamer over time. Eventually, humans felt comfortable around dogs — and dogs liked being around us — enough that we took them into our homes and recruited them for our hunts. Recent excavations at mammoth kill sites uncovered dog bones among the remains, suggesting that dogs and humans hunted together.

But even then, it's not clear that we loved dogs, Wynne said. That change happened around 10,000 years ago, when dogs started showing up in our artwork and burial grounds. Last year, scientists discovered an ancient cemetery near Siberia's Lake Baikal where 5,000- to 8,000-year-old dogs were buried right alongside their humans.

“You get dog burials, which show there was a lot of care and attention paid to the burial,” Wynne said, “and they include grave goods [valuable items placed in the grave for use in the afterlife], which really seems like there was a strong indication of affection.”

By ancient Egyptian times, household pets were laid to rest in elaborate tombs decorated with inscriptions, furnished with treasure and scented by incense. (Though archaeologists believe that some of the dogs were likely raised specifically to be killed, making the gesture seem somewhat less thoughtful.)

If dogs evolved to be the companions of human hunters, then cats came along to be farmers' pets. DNA evidence suggests that cats were first tamed by the Natu­fians, who lived in the Levant roughly 10,000 years ago and are often credited with being the inventors of agriculture. Cats, the logic goes, are very useful for catching the rodents that inevitably inhabit grain storehouses. As the animals started to congregate around human settlements, they became more social, developing the communication skills needed to deal with other cats and humans.

In the cases of both species, the process of domestication probably started with the animals themselves; tamer animals were better able to take advantage of the resources made available by human settlements. Then people got involved, selectively breeding the cutest, cuddliest and most cooperative creatures until we got the pets we know today.

So, that's how we came to love animals, but it still doesn't really explain why. We can't love dogs and cats simply because of their utility. For one thing, domesticated livestock are also useful, but we (typically) don't name cows or cry over movies about sheep that find their way home. For another, Wynne noted, dogs and cats really aren't that useful anymore.

“My own dog, who I love out of all proportion, is utterly and completely useless,” he said.

For several decades, it was believed that pet ownership was good for humans' physical and mental health. But with further research, the picture has become less clear. A 2009 study of nearly 40,000 people in Sweden found that pet owners suffered from more mental health problems than their non-pet-owning peers.

Other theories suggest that the benefit of pet ownership could have more to do with other humans. For example, pets might be what's called an “honest signal” of their humans' wealth, demonstrating that their owners have so much time and money to spare that they can afford to keep a creature whose purpose is only cuteness.

Then again, some argue that our love for pets is purely social, rather than biological. After all, a 2015 survey of more than 60 countries found that, even though dogs were kept in 52 countries, they were considered companions in fewer than half of them. Harold Herzog, a psychologist at Western Carolina University, has written that love for pets is a contagious habit we “catch” from our peers, as evidenced by the rise and fall of fads in dog breed ownership. Perhaps the warm and gooey feeling we get when we look into a puppy's eyes is just a consequence of social pressure and “Lassie Come Home.”

As a scientist, Wynne isn't happy with any of the theories put forward to explain our love for our pets. He'd like to see more and better data — perhaps an experiment that examined brain scans of people taken while they looked at cats and dogs.

But as someone who knows what it's like to love a dog, he was willing to indulge in some unscientific musing. Wynne noted that domesticated dogs are very childlike: They exhibit several behaviors usually found only among juveniles in wild animals, such as licking (or “kissing”) their owners' faces, and they're unable to survive on their own. When Wynne's family adopted their dog, his wife (“who is an engineer and very practical,” he said) remarked that perhaps they should have had more kids.

“She perceived that same buttons were being pressed that were pressed when we had our child,” Wynne said.

Maybe that's all there is to it: Humans are programmed to love soft and helpless things.

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